Do NowScientist Discovery

Hershey and Chase A. Analyzed DNA by X-Ray crystallography

Watson and Crick B. Proved that the nuclear material in a bacteriophage, not the protein coat infects a bacterium.

Rosalind Franklin C. Suggested the DNA structure of the double helix

Griffith D. Discovered transformation in bacteria

1. Match above.2. A court reporter types out a transcript

of the court proceedings. What does the underlined word mean?

RNA

Objectives

•SWBAT describe the 3 types of DNA.

•SWBAT describe the central dogma of biology

•SWBAT compare transcription in the prokaryote and eukaryote.

Children of the Night

• Xeroderma pigmentosum

• http://www.youtube.com/watch?v=WtLtByN1mQA

I. RNA Structure

•RNA= ribonucleic acid

•RNA is the 2nd type of nucleic acid– it is also made of millions of nucleotides

DNA RNA

• Double stranded

• Sugar: deoxyribose

• Adenine bonds to thymine

• Only one type of DNA per organism

• Single stranded

• Sugar: ribose

• No thymine! Adenine bonds instead to uracil

• 3 types of RNA

Types of RNAThere are 3 types of RNA:

• mRNA: messenger RNA, carries the information for protein synthesis

• rRNA: ribosomal RNA, makes the ribosomes in the cells functional. If there is no rRNA on the ribosomes, they won’t function

• tRNA: transfer RNA, takes amino acids from the cytoplasm to the ribosomes to make them into proteins

mRNA

rRNA

tRNA

Practice 1

• Which type of RNA is responsible for helping bring amino acids to make proteins?

• Which type of RNA makes up ribosomal subunits ?

• What type of RNA is this and what is it’s function?

Function of RNA• What does RNA actually do in the cell?

RNA helps make the proteins coded for by DNA

• To make proteins, the cell takes DNA, copies the sequence into an RNA copy and then makes proteins. This idea is called the Central Dogma

Central Dogma

RNA Transcription• How is the RNA Strand

Actually Made? Transcription

• Transcription= when you make an RNA copy of a sequence of DNA

• What enzyme is in charge of RNA transcription? RNA polymerase

•What nucleotide does RNA have instead of thymine?

RNA Transcription

•RNA transcription is very similar to DNA replication

•BUT! Instead of putting a Thymine (t) next to each Adenine (A), RNA Polymerase puts a Uracil (U) there

Practice

•What will the RNA strand be?

•DNA Strand:

TAAGCGCTCG

Transcription: Initiation

• Step 1: Initiation

RNA polymerase binds to a certain site on the DNA called the promoter and DNA strands unwind.

RNA polymerase starts to make RNA.

The stretch of DNA that is transcribed is called the transcription unit.

Transcription: Elongation

• Step 2: Elongation

• RNA polymerase adds nucleotides to the 3’end of the RNA molecule.

• *RNA polymerase can only add 5’ 3’

• The DNA double helix reforms as RNA polymerase moves away.

Transcription: Termination

• Step 3: Termination

A sequence eventually tells the RNA polymerase to stop.

The RNA polymerase falls off, and the mRNA transcript is created!

Animation

• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

Practice

• A DNA template strand has the following sequence: TACGGGATT. What is the mRNA sequence transcribed from the DNA?

• Arrange the flow of genetic information in the cell in order: 1. mRNA, 2. DNA, 3. protein.

• Come up with a way to remember the three steps of the transcription! (picture, saying, drawing) Be prepared to share out!

Where is this happening in the

cell? • What’s the main difference between

prokaryotic and eukaryotic cells?

Differences

Prokaryotic Transcription &

Translation

Eukaryotic mRNA modification

• After transcription, pre-mRNA in the nucleus is modified at BOTH ends.

• 5’ cap: adds a modified Guanine molecule, then 20-40 nucleotides

• Poly-A Tail: 50-250 Adenine nucleotides are added at the 3’ end

RNA Splicing• 8000 nucleotides 1200 nucleotides

(average)

• Introns: intervening sequences that are cut out of the pre-mRNA

• Exons: regions left in pre-mRNA to be made into proteins (eventually expressed)

Practice• Where does transcription happen in

prokaryotic cells?

• Where does transcription happen in eukaryotic cells?

• Which are the introns and exons in the following picture?

MIT OCW

• https://www.youtube.com/watch?v=tMr9XH64rtM

•Replicate:

TTTT

•Replicate:

ATCG

•Transcribe:

CGC

•Transcribe:

TAG

•Replicate:

GCGCGCG

•Transcribe:

GGTTAGC

•Replicate:

TAATAAG

•Transcribe:

AAA

•Transcribe:

GGG

•Transcribe:

ATGCG

•Replicate:

CCGGTTAA

•Replicate:

TATCGC

•Replicate:

ACGGTA

•Replicate:

TTACGA

•Replicate:

TATAGGC

•Transcribe:

GCGCGCG

•Transcribe:

CCGTAT

•Transcribe:

GTCGAG

•Transcribe:

TACCAG

RNA Translation

Objectives:

(1)SWBAT understand and describe the process of translation in the cells

Central Dogma

•DNA RNA ProteinsTranslation

Transcription

Translation•Translation: the process of

decoding mRNA into a polypeptide chain

•In translation, the information in a nucleic acid is converted into amino acids

•Which type of RNA is translated? mRNA

Translation• Where does RNA Transcription

happen? The same place as DNA replication the nucleus

Where does translation occur? On the ribosomes

Genetic Code•Genetic Code: the information that

the RNA carries that specifies the amino acids that will be made

•Every 3 nucleotides code for an amino acid. These 3 letter codes are called a codon.

•1 codon = 3 nucleotides = 1 amino acid AAA

CGA UGA

Practice

•Using the genetic code in your guided notes, what is the amino acid for the codon AGU?

SERINE

Practice 1

•Complete practice 1 on your worksheets

•Total time: 5 minutes

tRNA

•Who Can Remember?! What is the function of tRNA?

To transfer amino acids from the

cytoplasm to the ribosome

tRNA• tRNA has a

cloverleaf pattern

•At one end of the tRNA is the anticodon, it bonds with the codon in the mRNA (it is a complementary sequence)

tRNA• At the other end of the tRNA is the amino acid that the mRNA codes for

tRNA•Example: the mRNA codon is UUU (remember that RNA does not have thymine but has uracil instead)

What will be the anticodon for this mRNA?

What amino acid will be carried by this tRNA molecule?

AAA

phenylalanine

Steps of Translation

• Step 1: mRNA leaves the nucleus and attaches to the ribosome

• Step 2: tRNA brings specific amino acids to the RNA (according to the mRNA codons)

• Step 3: tRNA bonds to the mRNA and its amino acid attaches to the growing polypeptide chain

More Terms• The mRNA sequence is very long. How does

the cell know at which codon to start making the protein and which codon to stop?

• “Start” codon: This codon tells the protein chain to start building. The start codon is AUG or the amino acid methionine. Methionine is therefore the first amino acid in all proteins

• “STOP” codon: there are 3 stop codons: UAA, UGA and UAG

Transcription Game